This disclosure relates generally to the field of digital image processing. More particularly, this disclosure relates to auto-exposure bracketing operations. Many digital cameras provide a user with an auto-exposure bracketing (AEB) option. Under this option, a number of pictures (generally 3, 5 or 7) are captured at different exposures settings, which are typically uniformly spaced. Under extremely challenging imaging/auto-exposure conditions, users can employ the AEB option to increase the probability of acquiring an optimally exposed picture.
Another use of the AEB option is during high dynamic range (HDR) imaging. In order to create a high quality HDR image, the full dynamic range of a scene needs to be captured (specifically, highlight and shadow information). Unfortunately, the dynamic range of a scene often exceeds the dynamic range of the camera's imaging sensor, which are typically limited to capturing 256 (8 bits) to 1024 (10 bits) levels of brightness. In order to address this shortcoming, AEB may be employed. The most commonly employed brackets are: 2EV−, EV0, 2EV+ and 3EV−, EV0, 3EV+. Here, “EV” stands for exposure value and refers to a combination of the camera's shutter speed and aperture setting. The EV0 image refers to an image captured using an exposure value as determined by the camera's auto-exposure (AE) algorithm, EV− refers to an image captured at a lower stop (e.g., 2 or 3), and EV+ refers to an image captured at a higher stop (e.g., 2 or 3). In practice, fixed bracketing schemes (such as the two listed above), are not able to capture quality images for all possible illumination conditions. If the brackets are set too large, the likelihood of excessive noise and motion blur in the lower and upper bracketed images increases. If the brackets are set too small, the likelihood of clipped information in the lower and upper bracketed images increases.